1. Field of the Invention
The present invention relates generally to concrete screeds for consolidating and placing plastic concrete. In particular, the present invention relates to a lightweight, portable vibratory wet screed for leveling and consolidating plastic concrete. Relevant art may be found in U.S. Class 404, subclasses 101, 114, 115, as well as others.
2. Known Art
As will be appreciated by those skilled in the art, wet or plastic concrete must be worked before it sets and forms a hardened slab. Working plastic concrete generally involves consolidating the plastic concrete to evenly distribute water and aggregates throughout the resulting monolith and, subsequently, leveling the consolidated plastic concrete to appropriately contour the top layer of the plastic concrete.
Consolidating plastic concrete is often performed by vibrating the plastic concrete to evenly distribute water and aggregate materials throughout the monolith of concrete. The vibrations also fracture air pockets trapped inside the monolith and permit the air to escape therefrom. Other pockets of materials, such as sand and gravel or the like, are also shattered so that their components may be more evenly distributed throughout the monolith.
Several tools have been previously proposed for working plastic concrete. These tools include screeds, trowels (both manual and self-propelled), and placing tools such as floating pans and the like. Of the former, screeds with strike-offs are commonly employed during initial plastic concrete consolidation while the latter are typically used to finish the top surface of the concrete to a desired smoothness.
Screeds may generally be grouped as a)single operator tool, b) multiple operator tool, c) or a form riding tool. Screeds with strike-offs are normally employed in "wet" plastic concrete to initially level and consolidate the monolith because the wet plastic concrete typically will not support heavy weights. ("Wet" plastic concrete generally has a slump of between three and ten inches.)
Form riding tools are typically at least ten feet in length and ride upon the forms bounding the concrete monolith. These form-riding screeds and strike-offs are usually pulled along the form by a series of cables or the like and generally employ remote power to vibrate the blade. An example of a conventional form-riding screed is shown in U.S. Pat. No. 4,213,749.
Multiple operator screeds are shown in U.S. Pat. Nos. 4,798,494; 4,838,730; 4,752,156; and 4,701,071. These devices generally strike-off, vibrate and level plastic concrete in a single pass. They may employ remote power and are typically drawn through plastic concrete by multiple operators. However, they are large and unwieldy and they often require excessive site preparation and cannot be moved quickly about the pour. These devices also suffer from other handicaps associated with maintenance and the like.
Single operator screeds are often employed to strike-off, vibrate, and level plastic concrete in a single pass without form support. The portable nature of these devices permits their use about pour sites with minimal preparation and they are easy to transport. These devices are often advantageous in that they do not require significant preparation time and/or transport logistics. They are also highly maneuverable and typically require less maintenance than their larger counterparts.
U.S. Pat. No. 5,540,519 shows a portable, vibratory wet screed, the teachings of which are hereby expressly incorporated by reference. The portable screed shown therein is adapted to strike-off, vibrate and level wet concrete quickly and efficiently. However, the device is often subject to undesirable downtime at the pour site as a result of its complex vibratory dispersion system. Further, the invention is prone to suffer from undesirable penetration of the gear box structure resulting from the placement of the gearbox in the screed bar.
Thus, there exists a need in the art for a portable vibratory screed that may be easily transported about a pour site with minimal preparation to consolidate and level plastic concrete. In particular, a desirable device would enable an operator to begin levelling wet, plastic concrete immediately after pouring. A particularly advantageous device would use a dependable vibratory dispersion system to prevent undesirable down time while promoting efficient concrete consolidation and levelling.